Adaptive puncturing technique for multicarrier systems

ABSTRACT

Various embodiments are described for adaptive puncturing techniques.

BACKGROUND INFORMATION

Multicarrier communications may be described as a communicationstechnique in which multiple carriers or subcarriers are used tocommunicate information. As an example of multicarrier communications,Orthogonal Frequency Division Multiplexing (OFDM) may be described as acommunications technique that divides a communications channel into anumber of spaced frequency bands. In OFDM, a subcarrier carrying aportion of the user information may be transmitted in each band. InOFDM, each subcarrier may be orthogonal, differentiating OFDM from thecommonly used frequency division multiplexing (FDM). An OFDM symbol mayinclude, for example, a symbol transmitted simultaneously on each of theOFDM subcarriers during the OFDM symbol period. These individual symbolsmay be referred to as subcarrier symbols.

Some communication systems may include features that may adapt to sometypes of changing conditions. For example, some systems allow a datatransmission rate to be adjusted based upon a detected transmissioncondition. However, some types of adaptive systems can be complex orexpensive. A need exists for an improved adaptive system

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationsystem in accordance with one embodiment of the invention.

FIG. 2 is a block diagram of a wireless transceiver according to anexample embodiment.

FIG. 3 is a diagram illustrating a number of puncturing patternsaccording to an example embodiment.

DETAILED DESCRIPTION

In the detailed description, numerous specific details are set forth inorder to provide a thorough understanding of the embodiments of theinvention. It will be understood by those skilled in the art, however,that embodiments of the invention may be practiced without thesespecific details. In other instances, well-known methods, procedures andtechniques have not been described in detail so as not to obscure theforegoing embodiments.

Some portions of the detailed description that follows are presented interms of algorithms and symbolic representations of operations on databits or binary digital signals within a computer memory. Thesealgorithmic descriptions and representations may be the techniques usedby those skilled in the data processing arts to convey the substance oftheir work to others skilled in the art.

An algorithm is here, and generally, considered to be a self-consistentsequence of acts or operations leading to a desired result. Theseinclude physical manipulations of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. It has proven convenient at times,principally for reasons of common usage, to refer to these signals asbits, values, elements, symbols, characters, terms, numbers or the like.It should be understood, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities.

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions utilizing terms such as processing, computing, calculating,determining, or the like, refer to the action or processes of a computeror computing system, or similar electronic computing device, thatmanipulate or transform data represented as physical, such aselectronic, quantities within the registers or memories of the computingsystem into other data similarly represented as physical quantitieswithin the memories, registers or other such information storage,transmission or display devices of the computing system.

Embodiments of the present invention may include apparatuses forperforming the operations herein. This apparatus may be speciallyconstructed for the desired purposes, or it may comprise a generalpurpose computing device selectively activated or reconfigured by aprogram stored in the device. Such a program may be stored on a storagemedium, such as, but is not limited to, any type of disk includingfloppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-onlymemories (ROMs), random access memories (RAMs), electricallyprogrammable read-only memories (EPROMs), electrically erasable andprogrammable read only memories (EEPROMs), flash memory, magnetic oroptical cards, or any other type of media suitable for storingelectronic instructions, and capable of being coupled to a system busfor a computing device.

The processes and displays presented herein are not inherently relatedto any particular computing device or other apparatus. Various generalpurpose systems may be used with programs in accordance with theteachings herein, or it may prove convenient to construct a morespecialized apparatus to perform the desired method. The desiredstructure for a variety of these systems will appear from thedescription below. In addition, embodiments of the present invention arenot described with reference to any particular programming language. Itwill be appreciated that a variety of programming languages may be usedto implement the teachings of the invention as described herein.

In the following description and claims, the terms coupled andconnected, along with their derivatives, may be used. In particularembodiments, connected may be used to indicate that two or more elementsare in direct physical or electrical contact with each other. Coupledmay mean that two or more elements are in direct physical or electricalcontact. However, coupled may also mean that two or more elements maynot be in direct contact with each other, but yet may still cooperate orinteract with each other.

It is worthy to note that any reference in the specification to “oneembodiment” or “an embodiment” means in this context that a particularfeature, structure, or characteristic described in connection with theembodiment may be included in at least one embodiment of the invention.The appearances of the phrase “in one embodiment” or “an embodiment” invarious places in the specification do not necessarily refer to the sameembodiment, but may be referring to different embodiments.

It should be understood that embodiments of the present invention may beused in a variety of applications. Although the present invention is notlimited in this respect, the circuits disclosed herein may be used inmany apparatuses such as in the transmitters and receivers of a radiosystem. Radio systems intended to be included within the scope of thepresent invention include, by way of example only, wireless local areanetworks (WLAN) devices and wireless wide area network (WWAN) devicesincluding wireless network interface devices and network interface cards(NICs), base stations, access points (APs), gateways, bridges, hubs,cellular radiotelephone communication systems, satellite communicationsystems, two-way radio communication systems, one-way pagers, two-waypagers, personal communication systems (PCS), personal computers (PCs),personal digital assistants (PDAs), and the like, although the scope ofthe invention is not limited in this respect.

As used herein, the term packet may include a unit of data that may berouted or transmitted between nodes or stations or across a network. Asused herein, the term packet may include frames, protocol data units orother units of data. A packet may include a group of bits, which mayinclude one or more address fields, control fields and data, forexample. A data block may be any unit of data or information bits.

Referring to the Figures in which like numerals indicate like elements,FIG. 1 is a diagram illustrating an example of a wireless communicationsystem in accordance with one embodiment of the invention. In thecommunications system 100 shown in FIG. 1, a user wireless system 116may include a wireless transceiver 110 coupled to an antenna 117 and toa processor 112. Processor 112 in one embodiment may comprise a singleprocessor, or alternatively may comprise a baseband processor and anapplications processor, although the scope of the invention is notlimited in this respect. According to one embodiment, processor 112 mayinclude a baseband processor and Medium Access Control (MAC).

Processor 112 may couple to a memory 114 which may include volatilememory such as DRAM, non-volatile memory such as flash memory, oralternatively may include other types of storage such as a hard diskdrive, although the scope of the invention is not limited in thisrespect. Some portion or all of memory 114 may be included on the sameintegrated circuit as processor 112, or alternatively some portion orall of memory 114 may be disposed on an integrated circuit or othermedium, for example a hard disk drive, that is external to theintegrated circuit of processor 112, although the scope of the inventionis not limited in this respect. According to one embodiment, softwaremay be provided in memory 114 to be executed by processor 112 to allowwireless system 116 to perform a variety of tasks, some of which may bedescribed herein.

Wireless system 116 may communicate with an access point (AP) 128 (orother wireless system) via wireless communication link 134, where accesspoint 128 may include at least one antenna 118. Antennas 117 and 118 mayeach be, for example, a directional antenna or an omni directionalantenna, although the invention is not limited thereto. Although notshown in FIG. 1, AP 128 may, for example, include a structure that issimilar to wireless system 116, including a wireless transceiver, aprocessor, a memory, and software provided in memory to allow AP 128 toperform a variety of functions. In an example embodiment, wirelesssystem 116 and AP 128 may be considered to be stations in a wirelesscommunication system, such as a WLAN system.

Access point 128 may be coupled to network 130 so that wireless system116 may communicate with network 130, including devices coupled tonetwork 130, by communicating with access point 128 via wirelesscommunication link 134. Network 130 may include a public network such asa telephone network or the Internet, or alternatively network 130 mayinclude a private network such as an intranet, or a combination of apublic and a private network, although the scope of the invention is notlimited in this respect.

Communication between wireless system 116 and access point 128 may beimplemented via a wireless local area network (WLAN), for example anetwork which may be compliant with an Institute of Electrical andElectronics Engineers (IEEE) standard such as IEEE 802.11a, IEEE802.11b, IEEE 802.11g, IEEE 802.11n, IEEE 802.15, IEEE 802.16 and so on,although the scope of the invention is not limited in this respect.

In another embodiment, communication between wireless system 116 andaccess point 128 may be implemented via a cellular communication networkcompliant with a 3GPP standard, although the scope of the invention isnot limited in this respect.

One or more aspects of the invention may be applied to single carriersystems where information may be transmitted over a single carrier.Alternatively, one or more aspects of the invention may be applied tomulticarrier systems, such as an OFDM (Orthogonal Frequency DivisionMultiplexing) system for example, where information may be transmittedover multiple carriers or subcarriers, although the invention is notlimited in this regard.

FIG. 2 is a block diagram of a wireless transceiver according to anexample embodiment. Referring to FIG. 2, transceiver 200 may include atransmitter 201 to transmit information and a receiver 231 to receiveinformation. Transceiver 200 may include an adaptive bit loading block205 that may receive channel state information 203. Channel stateinformation 203 may include a signal-to-noise ratio (SNR), a bit errorrate (BER), a packet error rate, a channel estimate or channel transferfunction, etc., or other information that may describe a channeltransmission condition.

Adaptive bit loading block 205 may adaptively select a modulation scheme206 and a puncturing pattern 207 to be used by at least transmitter 201based upon the channel state information 203. According to an exampleembodiment, puncturing block 215 may discard some of the coded bits inaccordance with the puncturing pattern 207. Therefore, puncturing mayincrease the code rate since according to an example embodiment, a coderate may be considered to be a ratio of data bits/code bits.

Instead of selecting a puncturing pattern, adaptive bit loading block205 may alternatively first select a desired code rate based on thechannel state information, and then select a puncturing pattern toachieve the selected code rate given the mother code rate provided bycoder 210. In this example embodiment, adaptive bit loading block 205may also select a modulation scheme based on the channel stateinformation.

According to an example embodiment, channel state information 203 may beprovided for each of a plurality of OFDM subcarriers. Adaptive bitloading block 205 may select a modulation scheme 206 and a code rateand/or puncturing pattern 207 for each OFDM subcarrier based upon thechannel state information of the corresponding subcarrier.

According to an example embodiment, the modulation scheme 206 and thepuncturing pattern 207 may be varied for each OFDM subcarrier (on a persubcarrier basis). In another embodiment, the OFDM subcarriers may besplit into blocks of two or more adjacent subcarriers, referred to assubbands. The same modulation scheme and same puncturing pattern (ordesired code rate) may be selected for each subband (e.g., samemodulation scheme and same puncturing pattern for all subcarriers of asubband), although the invention is not limited thereto.

In selecting a modulation scheme and puncturing pattern for a subband,channel state information for one or more subcarriers in the subband maybe used to select these parameters for the subband. For example, thelowest SNR may be used (e.g., the lowest SNR for the subcarriers in thesubband), the average SNR for all subcarriers in the subband may beused, or other technique. These are some examples, and the invention isnot limited thereto.

A variety of different modulation schemes may be used. For example thefollowing modulation schemes may be used: binary phase-shift keying(BPSK), quadrature phase shift keying (QPSK), Quadrature AmplitudeModulation (QAM) such as 16-QAM (16 different symbols), 64-QAM (64different symbols), 256 QAM, etc., although the invention is not limitedthereto. Other modulation schemes may be used.

Coding may involve coding data bits using a coding technique (such asconvolutional coding, etc.) to produce coded bits or code bits.Puncturing may include, for example, dropping or discarding or nottransmitting certain coded bits to increase the code rate. Puncturingmay be used, for example, where an existing encoder uses a particularcode rate, and it may be desirable to increase the code rate by droppingor not transmitting one or more code bits. At the receiving node, thereceiver or demodulator may insert one or more dummy bits in place ofthe omitted (punctured) bits, and then decode the message.

According to an example embodiment, higher modulation schemes and highercode rates (e.g., through more puncturing) may correspond to higher SNRs(or better channel transmission conditions generally). According to anexample embodiment, if the channel state information, such as SNR for asubcarrier corresponds to a first SNR range, a first modulation schemeand a first puncturing pattern may be selected for that subcarrier orsubband for the transmission of data. If the SNR corresponds to a secondSNR range, then a second modulation type and a second puncturing patternmay be selected for transmission of data. These are just some examplesand the invention is not limited thereto.

The selected modulation scheme 206 and puncturing pattern 207 may alsobe provided to receiver 231 to select these parameters for demapping andde-puncturing of received information, although these parameters mayalternatively be selected by a remote transmitter for a receiver 231.

Transmitter 201 will now be described. An input bit stream 208 is inputat an encoder 210, which may be a convolutional encoder for example,although the invention is not limited thereto. Other types of coding maybe used. Encoder 210 may, for example, convolutionally encode the inputbit stream 208 using a mother code rate of ½, although the invention isnot limited thereto. Other mother code rates may be used. Encoder 210may output a coded bit stream 212.

The coded bit stream 212 may be input to a puncturing block 215.Puncturing block 215 may puncture the coded bit stream by dropping ordiscarding one or more coded bits according to a puncturing pattern 207specified by adaptive bit loading block 205 to produce a coded andpunctured data stream 217. Due to such puncturing, the (punctured) coderate for the punctured data stream 217 may be higher than the mothercode rate of the bit stream 212 output from encoder 210. Thus, each OFDMsubcarrier or subcarriers in each subband may be coded with a selectedcode rate (based on the puncturing pattern that is selected on a persubcarrier or per subband basis).

Mapping block 220 may then extract a number of bits from bit stream 217and maps the bits to a corresponding symbol of a selected modulationscheme. In an example embodiment, mapping block may extract or select anumber of bits in punctured bit stream 217 and maps the bits to acorresponding subcarrier symbol of the selected modulation scheme foreach (or at least some) of the subcarriers of the OFDM symbol. Thismapping may be repeated for a plurality of OFDM symbols. Modulationblock 225 may then perform OFDM modulation to generate modulated dataoutput 226 for transmission.

Receiver 231 in FIG. 2 will now be described. Modulated data 229 isreceived and OFDM demodulated by demodulation block 230 to output mapped(demodulated) data 232. Demapping block 235 demaps OFDM subcarriersymbols to demapped data bits 237. According to an example embodiment,depuncturing block 240 depunctures the demapped data by inserting dummybits at the appropriate locations based on the puncturing pattern 207 tooutput bit inserted (depunctured) data 242. This recovers the mothercode. Decoder 245 may then decode the depunctured data 242 to generatean output bit stream 247. According to an example embodiment, if aconvolutional encoder is used to encode the data at the transmit end, aViterbi decoder may be used for example as the decoder 245, although theinvention is not limited thereto.

FIG. 3 is a diagram illustrating a number of puncturing patternsaccording to an example embodiment, although the invention is notlimited to this format or type of puncturing patterns. In this example,convolutional codes with a rate of (n−1)/n may be formed from puncturinga mother code having a code rate=1/2 convolutional code, although theinvention is not limited thereto. Other codes or code rates may be used.In an example embodiment, the mother code may be generated with a codeconstraint length of 7, and using generator polynomials of G₁=133₈ andG₂=171₈, as examples. However, the invention is not limited thereto.

Several example puncturing patterns are shown in FIG. 3. As shown inFIG. 3, at 305, the mother code is shown, with one data bit being codedas two code bits, producing a mother code rate=½. No puncturing isperformed for pattern 305.

At 310, two data bits are encoded as four code bits (mother coderate=½). The four bits may be referred to as input coded bits for thepuncturing pattern. The puncturing pattern 310 shows that one of thefour input coded bits is discarded, resulting in a code rate of 2/3 (twodata bits being encoded as three code bits). The grayed out bit 312 inthe puncturing pattern 310 is discarded (punctured). The three white(non-discarded) bits may be referred to as the output coded bits of thepuncturing pattern.

At 315, three data bits are encoded as six code bits (mother coderate=½). A code rate of ¾ is achieved by discarding two of the six codebits (three data bits encoded as four code bits), as shown by thepuncturing pattern 315. Therefore, there are four output coded bits inthis puncturing pattern in 315.

At 320, five data bits are encoded as 10 code bits (mother code rate=½).Four of the 10 input coded bits are discarded as shown by the puncturingpattern 320, resulting in a code rate of 5/6 (five data bits encoded as6 code bits). There are six output coded bits for this puncturingpattern.

At 325, seven data bits are encoded as 14 code bits or input coded bits(mother code rate=½). Six of the 14 input coded bits are discarded asshown by the puncturing pattern 320, resulting in a code rate of 7/8(seven data bits encoded as eight code bits). Therefore, there are eightoutput coded bits for this puncturing pattern.

Table 1 below illustrates some parameters that may be used for anadaptive puncturing scheme according to an example embodiment. A numberof parameters are shown in the columns of Table 1, including themodulation type, number of bits per OFDM subcarrier (modulation) symbol,resulting code rate (after puncturing), the number of data bits persubcarrier symbol (after puncturing) for both single carrier bit loadingand subband bit loading (2 subcarriers per subband in this example), andthe data rate in Mbits/s for an example 20 MHZ channel having 48 OFDMsubcarriers, although the invention is not limited thereto. Other datarates, channel sizes, and other parameters may be used.

TABLE 1 Example 20 MHz channel adaptive puncturing scheme parametersModulation and Coding parameters Puncturing Data Output Single Two RateLength carrier Subcarriers Mbits/s (number of BL Subband 20 Mhz Numberoutput Number of BL 48 Data Of coded bits data bits Number ofsubcarriers Bits per Code in per data bits per (802.11a timing-Modulation Modulation Rate puncturing modulation modulation related Typesymbol (R) pattern) symbol symbol parameters) BPSK 1 1/2 2 — 0.5 6 QPSK2 1/2 2 1 1 12 QPSK 2 3/4 4 — 1.5 18  16 QAM 4 1/2 2 2 2 24  16 QAM 43/4 4 3 3 36  16 QAM 4 7/8 8 — 3.5 42  64 QAM 6 2/3 3 4 4 48  64 QAM 63/4 4 — 4.5 54  64 QAM 6 5/6 6 5 5 60 256 QAM 8 3/4 4 6 6 72 256 QAM 87/8 8 7 7 84

According to an example embodiment, it may be desirable in some cases tohave the number of modulation bits in a single OFDM subcarrier symbol(if adaptive bit loading per subcarrier is performed) or in thesubcarrier symbols of a single subcarrier subband (if adaptive bitloading per subband is performed) to be the same or a multiple (e.g.,2×, 3×, . . . ) of the number of output coded bits in a puncturingpattern that is used. For example, a puncturing processing may beperformed on a set of input coded bits (see, e.g., FIG. 3). For example,as shown in FIG. 3, a code rate R=3/4 puncturing pattern may need 6input coded bits from the mother code (R=½). Puncturing block 215discards 2 bits from this set of input coded bits, e.g., in positions asindicated by the puncturing pattern. In this example, the number ofoutput coded bits in the puncturing pattern is equal to 4 (this is anumber of “white squares” in puncturing pattern, shown in FIG. 3).

In an example embodiment, it may be desirable to map a set of outputcoded bits from the puncturing pattern (or a multiple of the outputcoded bits of the puncturing pattern) to a subcarrier symbol in one OFDMsubcarrier (e.g., if adaptive bit loading is used for individualsubcarriers) or to the subcarrier symbols in one subband (e.g., ifadaptive bit loading is used for subcarrier subbands), because anadjacent OFDM subcarrier or subband of subcarriers may have another coderate (e.g., use a different puncturing pattern). Therefore, in oneexample embodiment, to allow the output coded bits from a puncturingpattern to be mapped or modulated onto a single subcarrier or a singlesubband, it may be advantageous for the number of bits in one OFDMsubcarrier symbol (e.g., if adaptive bit loading per subcarrier isperformed) or the number of bits in subcarrier symbols in one subband(e.g., if adaptive bit loading per subband is performed) to be the sameor a multiple (e.g., 2×, 3×, . . . ) of the number of output coded bitsof the puncturing pattern that is used.

As an additional example, referring to Table 1, a 16 QAM modulationscheme uses four bits per subcarrier symbol. If a code rate (afterpuncturing) ¾ is used, this results in four output coded bits in thepuncturing pattern, which is the same as the number of bits (4) persubcarrier symbol for 16 QAM. This also transmits an integer number ofdata bits per OFDM subcarrier symbol. In this example, there will be 4code bits per subcarrier symbol, and 3 data bits per subcarrier symbol(due to ¾ code rate and 16 QAM modulation for this subcarrier).

Likewise, if 16 QAM modulation scheme is used, but with a code rate=7/8,this results in 8 output coded bits in the puncturing pattern. The 16QAM modulation uses 4 bits per subcarrier symbol. Therefore, a subbandof two 16 QAM subcarriers (8 bits total across two subcarrier symbols inthe subband) can accommodate (is the same number of bits as) the 8output coded bits from the puncturing pattern. Thus, a two subcarriersubband works well for this 16 QAM, R=7/8 example. These are justexamples and the invention is not limited thereto.

Note that for adaptive bit loading for single subcarrier, adaptivepuncturing allows use of data bits per subcarrier symbol in the range 1to 7, but does not (according to this example embodiment) allow use ofthe most robust BPSK modulation, as shown in Table 1, although theinvention is not limited thereto. In this example, using 2 subcarriersubband adaptive bit loading allows use of data bits per subcarrier inthe range 0.5 to 7 (also in finer granularity, e.g., steps of 0.5 databits) as well as use of BPSK, as shown in Table 1. Therefore, in somecases, subcarrier subband adaptive bit loading may have advantages oversingle subcarrier adaptive bit loading. These are just some examples andthe invention is not limited thereto.

It may also be advantageous to select a modulation scheme and apuncturing pattern (or code rate) where an integer number of data bitswill be mapped onto a single subcarrier symbol (for single subcarrieradaptive bit loading). Examples where this occurs in Table 1 include aQPSK modulation scheme with a code rate of ½, resulting in 1 data bitper subcarrier symbol, and 16QAM with a code rate of ¾, resulting in 3data bits per subcarrier symbol. Note, in table 1, a dash in the columnentitled “number of data bits per [subcarrier] modulation symbol”indicates where an integer number of data bits does not map to asubcarrier symbol for those parameters.

Note that each of the combinations of modulation types and code ratesshown in Table 1 may allow an integer number of data bits to be encodedon a 2 subcarrier subband. For example, 16QAM modulation with a coderate=7/8 provides 3.5 data bits per subcarrier symbol, and therefore 7data bits per subband (two subcarriers per subband). These are justadditional examples and the invention is not limited thereto.

While certain features of the embodiments of the invention have beenillustrated as described herein, many modifications, substitutions,changes and equivalents will now occur to those skilled in the art. Itis, therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the embodiments of the invention.

1. An apparatus comprising: an adaptive bit loading block to receive channel state information for a plurality of subcarriers and to select a modulation scheme and a puncturing pattern for each of the plurality of subcarriers or for each of a plurality of subbands based on the channel state information; a puncturing block to puncture a coded bit stream for each of a plurality of subcarriers or subbands in accordance with the selected puncturing pattern; a mapping block to map a coded and punctured bit stream output from the puncturing block to one or more subcarrier symbols for each of the plurality of subcarriers or subbands.
 2. The apparatus of claim 1 and further comprising an encoder coupled to the puncturing block to produce the encoded bit stream.
 3. The apparatus of claim 2 wherein the encoder comprises a convolutional encoder.
 4. The apparatus of claim 1 wherein each of the subbands comprises a plurality of subcarriers.
 5. The apparatus of claim 1 wherein the mapping block comprises a mapping block to map a coded and punctured bit stream output from the puncturing block to one or more OFDM subcarrier symbols for each of a plurality of OFDM subcarriers or OFDM subcarrier subbands, where the OFDM subcarrier subbands comprises a plurality of OFDM subcarriers.
 6. The apparatus of claim 1 and further comprising an OFDM modulator to modulate a selected subcarrier symbol onto a OFDM subcarrier for each of a plurality of OFDM subcarriers.
 7. The apparatus of claim 1 wherein the puncturing pattern and/or modulation scheme for a subcarrier are selected such that the number of bits in the subcarrier symbol or subband are the same or a multiple of a number of output coded bits in a puncturing pattern.
 8. The apparatus of claim 1 wherein a puncturing pattern and/or modulation scheme are selected such that one or more sets of output coded bits in a puncturing pattern may map onto one subcarrier or one subband.
 9. The apparatus of claim 1 wherein a puncturing pattern and/or modulation scheme are selected such that one or more sets of output coded bits in a puncturing pattern may map onto one subcarrier if adaptive bit loading per subcarrier is performed, or map onto one subband if adaptive bit loading per subband is performed.
 10. An apparatus comprising an adaptive bit loading block to select a modulation scheme an/or a puncturing pattern for an OFDM subcarrier or an OFDM subcarrier subband based on subcarrier channel state information.
 11. The apparatus of claim 10 wherein the modulation scheme and the puncturing pattern are selected such that a number of bits in an OFDM subcarrier symbol or in an OFDM subcarrier subband to be the same or a multiple of the number of output coded bits in the puncturing pattern.
 12. An apparatus comprising an adaptive bit loading block to select a modulation scheme and a puncturing pattern for each of a plurality of OFDM subcarriers or OFDM subcarrier subbands based on subcarrier channel state information, a subcarrier subband comprising a plurality of OFDM subcarriers.
 13. The apparatus of claim 12 and further comprising a puncturing block to puncture a coded bit stream for each of a plurality of the subcarrier subbands according to the puncturing pattern selected for the subcarrier subband.
 14. The apparatus of claim 13 and further comprising a mapping block to map coded and punctured bits into OFDM subcarrier symbols according to the selected modulation scheme for each of the subcarrier subbands.
 15. A method comprising: receiving channel state information for each of a plurality of subcarriers; and selecting a modulation scheme and a puncturing pattern for each of a plurality of subcarriers or subcarrier subbands based on the subcarrier channel state information.
 16. The method of claim 15 and further comprising: coding data bits to produce a coded bit stream; puncturing the coded bit stream for each of a plurality of subcarriers according to the selected puncturing pattern for each subcarrier; and mapping bits from the coded and punctured bit stream to subcarrier symbols according to the selected modulation schemes for each subcarrier or subband.
 17. The method of claim 15 wherein the selecting comprises selecting a modulation scheme and a puncturing pattern for each of a plurality of subcarriers or subcarrier subbands such that a number of bits in an OFDM subcarrier symbol or OFDM subcarrier subband is the same or a multiple of the number of output coded bits in a puncturing pattern.
 18. A method comprising: receiving channel state information for each of a plurality of subcarriers; and selecting a modulation scheme and a puncturing pattern for each of a plurality of subcarrier subbands based on the subcarrier channel state information, each subband comprising a plurality of OFDM subcarriers. 